Indicator for use in vehicles having an energy storage device

ABSTRACT

An indicator to indicate an amount of power available from an energy storage device. The indicator normalizes raw power values to values which are understood by the driver. The indicator indicates the normalized values to facilitate making a driving decision.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to an indicator for use in vehicles havingan energy storage device. The indicator indicates an amount of poweravailable from the energy storage device.

2. Background Art

A hybrid electric vehicle (HEV) includes at least a primary power sourceand a secondary power source. Typically, the primary power source is afuel cell, an engine, or other energy generating device, and thesecondary power source is a battery or other energy storing device.

The secondary power source, such as the battery, can be used to provideenergy to an electric motor or other electric device for electricassist. The electric assist generally includes providing torque fordriving the vehicle. The electric assist torque can supplement torqueprovided by the primary power source, it can be the sole source oftorque, or it can used to engage an electric four-wheel drive system.

The secondary power source stores energy as opposed to generatingenergy. As such, the amount of energy the secondary power source canprovide for generating torque is limited to its stored energy.

It is desirable to indicate to the driver the amount of stored energyavailable from the secondary power source. As such, there exists a needto indicate an amount of power available from the energy storage device.

SUMMARY OF INVENTION

The present invention addresses the need identified above with anindicator. The indicator indicates an amount of power available from anenergy storage device. The indicator normalizes raw energy values tovalues which are understood by the driver.

One aspect of the present invention relates to an indicator system in avehicle having an energy storage device that contributes power to anelectric assist device. The indicator can be used with any electricassist device in the vehicle that can be used for providing torque.

The system can be used with traction motors in a series hybrid electricvehicle (SHEV), a parallel hybrid electric vehicle (PHEV), and apowersplit hybrid electric vehicle (PSHEV). In addition, the indicatorcan be used with electric four-wheel drive vehicles where a batterypowers an electric motor used to optionally drive normally non-drivenwheels of a two-wheel drive vehicle in order to provide electricfour-wheel drive.

The system includes a processing source to calculate a normalized amountof power available from the energy storage device. In addition, thesystem includes an indicator to indicate the normalized amount of poweravailable from the energy storage device so that the driver can view theindicator.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an exemplary hybrid electric vehicle system having anindicator in accordance with the present invention;

FIG. 2 illustrates one embodiment of the indicator providing apercentage display in accordance with the present invention;

FIG. 3 illustrates a first flow chart for a first normalization methodwhich normalizes a battery state of charge in accordance with thepresent invention;

FIG. 4 graphically represents the first normalization method show inFIG. 3;

FIG. 5 illustrates a second flow chart for a second normalization methodwhich normalizes a battery discharge limit in accordance with thepresent invention;

FIG. 6 graphically represents the second normalization method show inFIG. 5;

FIG. 7 illustrates a third flow chart for a third normalization methodwhich normalizes a battery state of charge and a battery discharge limitin accordance with the present invention;

FIG. 8 illustrates one embodiment of the indicator providing a rangedisplay in accordance with the present invention;

FIG. 9 illustrates one embodiment of the indicator providing an electricassist available display in accordance with the present invention;

FIG. 10 illustrates a fourth flow chart for a fourth normalizationmethod which normalizes a battery discharge limit based on a batterytemperature threshold in accordance with the present invention; and

FIG. 11 graphically represents the fourth normalization method show inFIG. 10.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary hybrid vehicle that is commonly referredto as a powersplit hybrid vehicle (PSHEV) system 10. The system 10includes an engine 14, a transmission 16, and a battery 20 which operatewith a planetary gear set 24, a generator 26, a motor 28, and meshinggears 32 to provide the torque. The torque is received by a torque shaft36 for transfer to a differential axle 38 mechanism for final deliveryto wheels 40.

The present invention can be used with any hybrid system which includesthe battery or other energy storage device to provide power to theelectric assist device. In particular, the present invention can be usedwith a series hybrid electric vehicle (SHEV), a parallel hybrid electricvehicle (PHEV), and a powersplit hybrid electric vehicle (PSHEV). Inaddition, the system can be used with electric four-wheel drive vehicleswhere a battery powers an electric motor used to optionally drivenormally non-driven wheels of a two-wheel drive vehicle in order toprovide electric four-wheel drive. In the case of electric four-wheeldrive, the electric assist device may not couple to the transmission 18as shown.

A vehicle system controller 44 (VSC) selects the power and torquedelivery mode based on the vehicle operating conditions and a predefinedstrategy. To this end, the vehicle system controller 44 receives asignal from a transmission range selector 46 (PRND), accelerator pedalposition (APP) 48, a brake pedal position sensor 50 (BPPS), and abattery signal 68 indicating battery energy levels.

In response to the received signals, the vehicle system controller 44generates signals to the engine 14, a transmission control module 54(TCM), and a battery control module 56 (BCM). Theses signals include adesired engine torque 60, a desired wheel torque 62, a desired enginespeed 64, and a generator brake command 66. The modules then providefurther signal to control the hybrid vehicle, such as a generator brakecontrol 70, a generator control 72, and a motor control 74.

The use of the battery 20 to provide power to the motor 28 for drivingthe vehicle is commonly referred to as electric assist. The electricassist can be provide as the sole source or torque or in combinationwith torque provided by the engine 14.

The system 10 further includes a relative level indicator 82. The levelindicator 82 indicates an amount of power available from the battery 20,or other energy storage device that may be used, such as anultracapacitor, in place of the battery.

FIG. 2 illustrates a relative percentage indicator 84 in accordance withthe present invention. The relative percentage indicator 84 includes adisplayed level 86. The driver can view the displayed level 28 todetermine whether the battery 20 has sufficient power to conduct adesired driving operation. In this manner, the driver makes a drivingdecision based on the indicator 84. The displayed level 86 indicates thelevel relative to a full position 88 and an empty position 90.

The indicator 84 can be located on an instrument panel or in anotherarea viewable by the driver. The driver can view the indicator 84 andmay make a driving decision based on the level of indicated power. Thedisplayed level 28 corresponds with a normalized available power value.The normalized available power value is calculated by the vehicle systemcontroller 44 based on one of the number of normalization methods of thepresent invention.

In general, the displayed level 86 is a normalized value of theavailable battery power, typically a percentage. The percentage isnormalized because the actual or raw amount of power from the battery 20is not easily understood by the driver. In other words, the drivercannot easily understand how the battery's state of charge or dischargelimit affects the amount of power available from the battery. To addressthis problem, the present invention normalizes the amount of poweravailable from the battery according to one of the normalization methodsdisclosed below.

FIG. 3 is a flow chart that illustrates a first normalization method,which is referred to with reference numeral 92. The first normalizationmethod includes a step 94 to calculate a battery state of charge (SOC).The SOC is a raw percentage value that indicates how much power thebattery has stored relative to its fully charged state. The SOC is adynamic value derived from operating parameters, such as current,voltage, and temperature of the battery and changes relating to vehicleoperation. Accordingly, it is a raw value derived directly from thebattery prior to any normalization. The SOC decreases when the batteryis discharging, and the SOC increases when the battery is charging.

Step 96 calculates an SOC low limit value (SOC LLV) for the battery. TheSOC LLV corresponds with a minimum SOC the battery should maintain atall times to insure full discharge capability. The SOC LLV is selectedaccording to the type of battery and other factors, such as batterytemperature and battery age, or it can be calculated by the vehiclesystem controller 44.

Step 98 calculates a SOC minimum offset to the SOC LLV. The minimumoffset includes adding an SOC low offset limit (SOC LOL) to the SOC LLV.Addition of the SOC LOL to the SOC LLV increases the reserve amount ofstored power. The reserve amount of power is still available if needed,but it is not indicated to the driver. Preferably, the driver makes adriving decision without reliance on the reserve amount. The SOC LOLprovides additional protection to prevent over discharging of thebattery. The vehicle system controller 44 selects or calculates the SOCLOL.

Step 100 calculates a SOC maximum offset to the SOC LLV. The maximumoffset includes adding an SOC high offset limit (SOC HOL) to the SOCLLV. Much like the minimum offset, the maximum offset indicates amaximum useable amount of SOC. The maximum useable amount of SOC istypically less than the maximum capability of the battery. The SOC HOLis typically a numeric SOC value that corresponds with an idealized highlimit on SOC to prevent over charging. The maximum SOC offset istypically less than the battery's rated maximum SOC. The vehicle systemcontroller 44 can select or calculate the SOC HOL.

Step 100 normalizes the SOC calculated in step 40 for display to thedriver. The normalization includes adjusting the calculated SOC based onthe SOC LLV, SOC LOL, and SOC HOL. The normalized SOC becomes thedisplayed percentage. Equation (1) illustrates a formula for calculatingthe normalized SOC in accordance with the first normalization method.

$\begin{matrix}{{{Displayed}\mspace{14mu}{percentage}} = \frac{\left( {{{Calculated}\mspace{14mu}{SOC}} - {{Minimum}\mspace{20mu}{Offset}}} \right)}{\left( {{{Maximum}\mspace{20mu}{Offset}} - {{Minimum}\mspace{20mu}{Offset}}} \right)}} & (1)\end{matrix}$

FIG. 4 is a graphical representation of the first normalization method.The graph of FIG. 4 shows that the SOC LLV is 40%, the SOC LOL is 0%,and the SOC HOL is 40%. A calculated SOC of 40% is displayed as anormalized SOC percentage of 0%. A calculated SOC of 80% is displayed asa normalized SOC percentage of 100%. A calculated SOC in the range of40% to 80% is linearized and is displayed as a normalized SOC percentagein the range of 0% to 100%.

Returning to FIG. 3, an optional override step 104 permits overridingthe displayed percentage. The override forces the displayed percentageto 0% regardless of the normalized SOC. The override is triggered by thebattery's discharge limit (DCL). The DCL is a numerical parameter thatindicates how rapidly the battery can instantaneously discharge itsstored power. Like SOC, DCL is a dynamic value that changes as a resultof driving conditions or other vehicle conditions, such as batterytemperature.

The override includes monitoring whether DCL is lower than a predefinedDCL threshold. The DCL threshold corresponds with the inability of thebattery to instantaneously discharge sufficient power. The sufficientpower is a design parameter of the battery, but it generally correspondsto the point at which the decision to be made by the driver becomes moreaffected by the low DCL than the normalized SOC. The override isadvantageous because the SOC may be sufficient for conducting thedesired driving operation, but the DCL is so low that the battery cannotdischarge the desired power regardless of the SOC.

FIG. 5 is a flow chart that illustrates a second normalization methodthat is referred to with reference numeral 108. This normalizationmethod differs from normalization method illustrated by FIG. 3 in thatthe displayed percentage is a normalized DCL and the override istriggered by the calculated SOC.

Normalization method 108 includes a step 110 for calculating the DCL ofthe battery. The DCL is a percentage determined by the vehicle systemcontroller 44. The vehicle system controller calculates a DCL valuebased on operating parameters of the battery, such as current voltageand temperature, and divides the DCL value by a maximum, or rated, DCLvalue to determine the percentage value for the DCL.

Step 112 calculates a DCL low limit value (DCL LLV) for the battery. TheDCL LLV corresponds with a minimum DCL the battery should maintain toinsure minimum vehicle performance. The DCL LLV is selected according tothe type of battery and other factors, such as battery temperature,battery age, and battery SOC, or it can be calculated by the vehiclesystem controller 44.

Step 114 calculates a minimum offset to the DCL LLV. The minimum DCLoffset includes adding a DCL low offset limit (DCL LOL) to the DCL LLV.Addition of the DCL LOL to the DCL LLV additionally increases thereserve amount of power the battery should maintain. The reserve amountof power is still available if needed, but it is not indicated to thedriver. Preferably, the driver makes a driving decision without relianceon the reserve amount. The vehicle system controller selects orcalculates the DCL LOL.

Step 116 calculates a maximum DCL offset to the DCL LLV. The maximumoffset includes adding a DCL high offset limit (DCL HOL) to the DCL LLV.Much like the minimum offset, the maximum offset indicates a maximumuseable amount of DCL. The maximum useable amount of DCL is typicallyless than the maximum capability of the battery. The maximum DCL LLV istypically less than the rated maximum DCL. The vehicle system controllercan select or calculate the DCL HOL.

Step 118 normalizes the DCL calculated in step 62 for display to thedriver. The normalization includes adjusting the calculated DCL based onthe DCL LLV, DCL LOL, and DCL HOL. The normalized DCL becomes thedisplayed percentage. Equation (2) illustrates a formula to calculatethe normalized DCL in accordance with the second normalization method.

$\begin{matrix}{{{Displayed}\mspace{14mu}{percentage}} = \frac{\left( {{{Calculated}{\mspace{11mu}\;}{DCL}} - {{Minimum}\mspace{14mu}{DCL}{\mspace{11mu}\;}{Offset}}} \right)}{\left( {{{Maximum}\mspace{14mu}{DCL}\mspace{14mu}{Offset}} - {{Minimum}\mspace{14mu}{DCL}\mspace{20mu}{Offset}}} \right)}} & (2)\end{matrix}$

FIG. 6 is a graphical representation of the second normalization method.The graph of FIG. 6 shows that when the DCL LLV is 40%, the DCL LOL is0%, and the DCL HOL is 40%. As such, a calculated DCL of 40% isdisplayed as a normalized DCL percentage of 0%. A calculated DCL of 80%is displayed as a normalized DCL percentage of 100%. A calculated DCL inthe range of 0% to 40% is linearized and is displayed as a normalizedDCL percentage in the range of 0% to 100%.

Returning to FIG. 5, an optional override step 120 permits overridingthe displayed percentage. The override forces the displayed percentageto 0% regardless of the normalized DCL. The override is triggered by theSOC of the battery. The override includes monitoring whether SOC islower than a predefined SOC threshold. The predefined SOC thresholdcorresponds with the inability of the battery to provide sufficientpower to operate the vehicle. The low SOC threshold is a designparameter of the battery, but it generally corresponds to the point atwhich the decision to be made by the driver becomes more effected by thelow SOC than the normalized DCL. The override is advantageous becausethe DCL may be sufficient for conducting the desired driving operation,but the SOC may be so low that the battery cannot provide enough powerto achieve sustained vehicle performance regardless of the DCL.

FIG. 7 is a flow chart that illustrates a third normalization method,referred to with reference numeral 124. The third normalization methodincludes a step 126 to normalize SOC based on the normalization of SOCdisclosed in the normalization method described with reference to FIG. 3and equation (1). Step 128 corresponds with normalizing DCL based on thenormalization of DCL disclosed in the normalization method describedwith reference to FIG. 5 and equation (2). Step 130 determines a lowestnormalized percentage out of the normalized SOC and the normalized DCL.The displayed percentage becomes the lowest of the normalized SOC andDCL percentages.

FIG. 8 illustrates a range indicator 134 in accordance with one aspectof the present invention. The range indicator displays charge ranges 136of available battery power, such as a below-normal battery charge 138, anormal battery charge 140, and an above-normal battery charge 142. Therange indicated is selected according to percentage ranges assigned toeach range. The displayed percentage from the first normalizationmethod, the second normalization method, or the third normalizationmethod can be matched to one of the ranges.

For the first normalization method, the below-normal battery charge 138can correspond with a normalized SOC in the range of 0–25%, the normalbattery charge 140 can correspond with a normalized SOC in the range of25%–75%, and the above-normal battery charge 142 can correspond with anormalized SOC in the range of 75%–100%. In addition, hysteresis logicor an offset threshold can be included to prevent oscillations betweenthe different ranges. More or less ranges can be included, for example,rather than three ranges, indicators for low charge and normal chargecan be used.

FIG. 9 illustrates an electric assist unavailable indicator 146. Theelectric assist unavailable indicator 146 is a light that illuminatesbased on a normalized amount of power available from the battery. If thelight is illuminated, then electric assist is limited, and if the lightis unilluminated, then electric assist is available.

The indicator 146 can be particularly adapted to indicating theavailability of electric four-wheel drive assist in a vehicle havingnon-driven wheels which are driven by an electric motor to provideelectric four-wheel drive. In this case, a limit value would be set forindicating whether electric four-wheel drive is available. Preferably,the limit would be based on a normalized amount of available batterypower as described above.

The normalized amount of available power from the battery can bedetermined from one of the above-described normalization methods, oraccording to a fourth normalization method. The fourth normalizationmethod is graphically shown in FIG. 10.

The fourth normalization method 150 includes a step 152 for calculatingthe battery temperature of the vehicle. Step 154 calculates DCL asdescribed above. Step 156 compares DCL against the battery temperatureDCL threshold. The comparison step 156 is based on a graphical DCLtemperature threshold, as shown in FIG. 11.

If the DCL is greater than a DCL battery temperature threshold 158, thenelectric assist is available and the indicator 146 is non-illuminated,and if the DCL is less than the DCL ambient temperature threshold 158,then electric assist is unavailable and the indicator 146 isilluminated. In addition, hysteresis and offset logic 160 can optionallybe included to prevent oscillations. The hysteresis 160 operates toincrease a percentage of the DCL must exceed each time the calculatedDCL drops below the DCL ambient temperature threshold 112.

While the embodiment described above relates to an HEV, the presentinvention is not so limited. In contrast, the present invention operateswith any type of vehicle that relies on an energy storage device,whether the energy storage device is a battery, an ultra capacitor orother device, for at least a portion of the power used to drive thevehicle. In addition, the present invention is not limited to automotivevehicles. Rather, the present invention can operate with any type ofvehicle or vessel, such as boats and airplanes.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. In an electric vehicle having an energy storage device, an indicatorsystem comprising: a processing source to calculate a normalized amountof power available from the energy storage device, the normalized amountbeing calculated as a function of desired limits on operator use ofpower actually available from the energy source; an indicator toindicate the normalized amount of power available from the energystorage device; wherein the energy source is a battery which providespower for use in providing electric assist and the processing sourcecalculates the normalized amount of power available from the battery asa normalized battery state of charge (SOC) such that the indicatorindicates the normalized SOC; and wherein the normalized battery SOC iscalculated based in part on a calculated battery SOC, a minimum batterySOC offset, and a maximum SOC offset.
 2. The system of claim 1 whereinthe processing source further comprises a battery discharge limit (DCL)override, wherein the override forces the normalized battery SOC to zeroin response to the DCL being less than a predefined threshold.
 3. Thesystem of claim 1 wherein the normalized amount of power available fromthe energy storage device is a range selected from the group comprisingbelow-normal battery charge, normal battery charge, and above-normalbattery charge.
 4. The system of claim 3 wherein the range is based onthe normalized battery state of charge (SOC).
 5. The system of claim 3wherein the range is based on a normalized percentage discharge limit(DCL).
 6. The system of claim 3 wherein the indicator includes apercentage display for indicating the normalized amount of poweravailable from the energy storage device.
 7. The system of claim 1wherein the indicator includes an illuminable light that is illuminatedbased on the normalized amount of power available from the battery,wherein electric assist is unavailable if the light is illuminated andelectric assist is available if the light is unilluminated; and whereinthe normalized amount of power available from the energy storage deviceis a raw discharge limit (DCL) temperature based threshold, wherein thelight is unilluminated when the raw DCL is greater than the thresholdand the light is illuminated when the raw DCL is less than thethreshold.
 8. The system of claim 7 wherein the raw DCL temperaturebased threshold includes a hysteresis offset threshold such that the rawDCL must surpass the hysteresis offset threshold when the light isilluminated in order to unilluminate the light, wherein the hysteresisoffset threshold is greater than the raw DCL temperature basedthreshold.
 9. The system of claim 7 wherein the raw DCL temperaturebased threshold varies according to a battery temperature.
 10. In anelectric vehicle having an energy storage device, an indicator systemcomprising: a processing source to calculate a normalized amount ofpower available from the energy storage device, the normalized amountbeing calculated as a function of desired limits on operator use ofpower actually available from the energy source; an indicator toindicate the normalized amount of power available from the energystorage device; and wherein the energy source is a battery whichprovides power for use in providing electric assist and the processingsource calculates the normalized amount of power available from thebattery as a normalized battery discharge limit (DCL) such that theindicator indicates the normalized DCL.
 11. The system of claim 10wherein the normalized battery DCL is calculated based in part on acalculated battery DCL, a minimum battery DCL offset, and a maximum DCLoffset.
 12. The system of claim 11 wherein the processing source furthercomprises a battery state of charge (SOC) override, wherein the overrideforces the normalized battery DCL to zero in response to the DCL beingless than a predefined threshold.
 13. In an electric vehicle having anenergy storage device, an indicator system comprising: a processingsource to calculate a normalized amount of power available from theenergy storage device, the normalized amount being calculated as afunction of desired limits on operator use of power actually availablefrom the energy source; an indicator to indicate the normalized amountof power available from the energy storage device; and wherein theenergy source is a battery which provides power for use in providingelectric assist and the processing source calculates the normalizedamount of power available from the battery as a minimum percentageselected from the group comprising a normalized battery of state ofcharge (SOC) and a battery percentage discharge limit (DCL).
 14. Thesystem of claim 13 wherein the normalized battery SOC is calculatedbased in part on a calculated battery SOC, a minimum battery SOC offset,and a maximum SOC offset, and wherein the normalized battery DCL iscalculated based in part on a calculated battery DCL, a minimum batteryDCL offset, and a maximum DCL offset.
 15. A method to communicate anamount of available battery power to a driver of a vehicle havingelectric assist, wherein the amount of available battery power is usedby the driver to make a driving decisions with respect to electricassist, the method comprising: calculating a raw power value for thebattery based on operating parameters of the battery; normalizing theraw power value to produce a displayable power value, the normalizedpower value being determined as a function of desired limits on operatoruse of the raw power actually available from the battery; displaying thepower value in a position viewable by the driver; and wherein thedisplayable power value is a normalized battery state of charge (SOC)such that the indicator indicates the normalized SOC, wherein thenormalized battery SOC is calculated based in part on a calculatedbattery SOC, a minimum battery SOC offset, and a maximum SOC offset. 16.A method to communicate an amount of available battery power to a driverof a vehicle having electric assist, wherein the amount of availablebattery power is used by the driver to make a driving decisions withrespect to electric assist, the method comprising: calculating a rawpower value for the battery based on operating parameters of thebattery; normalizing the raw power value to produce a displayable powervalue, the normalized power value being determined as a function ofdesired limits on operator use of the raw power actually available fromthe battery; displaying the power value in a position viewable by thedriver; and wherein the displayable power value is a normalized batterycalculating discharge limit (DCL) such that the indicator indicates thenormalized DCL, wherein the normalized battery DCL is calculated basedin part on a calculated battery DCL, a minimum battery DCL offset, and amaximum DCL offset.